Synthetic test circuits are known from IEC publication 60427, third edition 2000-04, page 95, Figure BB1.
The “typical current injection circuit with voltage circuit in parallel with the test circuit-breaker” was developed in the early 1950s at the initiative of Professor J. Biermanns, who was then director of the new High-Voltage Institute of AEG in Kassel-Bettenhausen and was formerly director of the AEG-Transformatoren-Fabrik Oberschöneweide (“TRO”) in Berlin, to increase the direct testing capacity of the testing department of the Institute.
During the development work, this synthetic test circuit was known in the Institute as “artificial circuit”, and Mr. Biermanns, too, always called it the “artificial circuit”.
After the “artificial circuit” was put into operation in 1953, the development management of AEG in Frankfurt am Main renamed it the “Weil circuit” and later the “Weil-Dobke circuit,” as exemplified in the publications “The Weil-circuit, a circuit to be tested as a high-voltage circuit”, by E. Slamecka, in Proceedings from the Opening of the AEG-High-voltage Institute in Kassel, 1953, pp. 52–57, and “Investigation of the AEG test circuit for high-capacity circuit-breakers according to ‘Weil-Dobke’”, by E. Slamecka, dissertation thesis, Graz (Austria) Institute of Technology, 1955.
However, a more accurate analysis of the German patent specification 962 731 by Fritz Weil (“Weil '731”) describing a synthetic test circuit, and of German patent specification 975 303 by G. Dobke (“Dobke '303”), proves that the association of these names with the circuit was an oversight and, therefore, objectively unjustified.
The known prior art described in Weil '731, that is, the AEG “artificial circuit,” was mistakenly understood as the subject of his invention and thus erroneously connected with the name of Weil.
Also, Dobke '303, entitled “Supplement to Patent 962 731” (that is, Weil '731), according to disclosed principle and the represented current flow, represents the state of art described and to be improved in Weil '731, the same “artificial circuit” of AEG, and factually forms the patented subject of Weil's invention related back to this state of the art in 1942, invented by unknown inventors in the former TRO. This fact also was overlooked at that time and thus the “artificial circuit” of AEG obtained, again erroneously, the surname “Dobke”.
In Weil '731, it is said of the state of the art: “A known test arrangement of this type (“artificial circuit”) has the disadvantage that the characteristics of the primary current do not conform to the conditions of the natural test shortly before its zero crossing and the inception of high voltage as recovery voltage, respectively. This is the result of the circumstance that the high-voltage source is already switched to the test switching point before the primary current's zero crossing, so that both currents are superimposed in the breaker gap and result in too high a value.” To this, the present inventor adds: “The superimposition of current can also result in an under stressing of the test switch, if the high-voltage source current becomes zero too far away from primary current becoming zero.”
The IEC publication 60427, cited above in paragraph [0002], at page 23, indicates limiting values (without disclosing any relation) for the duration of the sole flow of the oscillatory current in the test switch—minimum 200 μs, maximum 500 μs—that should not be exceeded on either side. The publication does not provide information where an equivalence exists in the stress of the test switch in this synthetic test circuit and its stress in a direct test circuit and, if applicable, when (within this time interval) the zero current of the oscillatory current should occur.
During the synthetic test, the auxiliary switch does not relieve a superimposition of the high current with an oscillatory current of opposite polarity, which is a system-immanent characteristic of another known synthetic test circuit shown in IEC publication 60427 at page 97, Figure BB3 and Figure BB4. Therefore, with approximately the same current-breaking capacity of the auxiliary switch and the test switch, the arc voltages of the two switches are also about the same. These voltages in series in the high current circuit can substantially distort the high current.
The known remedy, a high-current transformer, to increase the source voltage in the high-current circuit, is costly and reduces its current yield.
As a result, this state of the art poses three unsolved objects for this invention. First, it asks to clarify whether the problem can be resolved, i.e., as a principle, can an equivalence exist in the loading of the test switch in this synthetic test circuit as compared with a direct test circuit? Second, it seeks to develop a method for determining a set value for the synthetic test circuit, at which the loading of this circuit is equivalent to the loading in a direct test circuit. And, third, it seeks to substantially reduce the loading of the auxiliary switch by arc energy emitted into the interrupter chamber in order to dispense with a high-current transformer with a simultaneously achieved substantially reduced interrupter effect and a corresponding lower arc voltage as well as current distortion.